The present invention relates to an environmental friendly vehicle. More particularly, the present invention relates to hybrid vehicles, such as hybrid electric vehicles (HEVs).
Hybrid electric vehicles include an internal combustion engine and at least one electric motor powered by a battery array. The HEV of the present invention uses an engine in combination with an electric motor. An energy storage device is also used to store energy for driving the electric motor. The engine, preferably in conjunction with a generator (for series drive embodiment or without for a parallel embodiment), and the energy storage device work in combination to provide energy for powering the vehicle motor. A series HEV typically uses an engine with a generator (APU/PPU) to supply electricity to the motor and the energy storage system. A parallel HEV has a direct mechanical connection between the engine and the wheels. The use of electric power substantially cuts down on chemical emissions and vastly improves fuel economy.
In a parallel type hybrid electric vehicle, both the internal combustion engine and the electric motor are coupled to the drive train via mechanical means. The electric motor may be used to propel the vehicle at low speeds and to assist the internal combustion engine at higher speeds. The electric motor may also be driven, in part, by the internal combustion engine and be operated as a generator to recharge the battery array.
In a series type hybrid electric vehicle, the internal combustion engine is used only to run a generator that charges the battery array. There is no mechanical connection of the internal combustion engine to the vehicle drive train. The electric traction drive motor is powered by the battery array and is mechanically connected to the vehicle drive train.
Although HEVs have been previously known, the HEV technology of the present invention provides significant advantages of providing a viable HEV technology that allows for a high performance HEV with a unique management of the charge and energy distribution system.
Other features of the invention will become apparent as the following description proceeds and upon reference to the drawings.
In general terms, the present invention includes an energy storage system, the energy storage system adapted to accept energy so as to be capable of discharging and accepting energy through a series of discharge and energy acceptance events, and having a maximum energy state level and an actual minimum energy state level; and wherein the power unit and the energy storage system provide electricity to the electric motor for powering the vehicle; and an energy storage controller programmed to control the energy storage system by setting an artificial minimum energy state level to an initial level above the actual minimum energy state level, and, during a series of discharge and energy acceptance events, to be able to adjust the artificial minimum energy state level such that:
(a) in the case where a discharge and energy acceptance event results in the acceptance of insufficient energy to replenish the energy storage system to the maximum energy state level, the artificial minimum energy state level is raised; and
(b) in the case where a discharge and energy acceptance event results in the acceptance of sufficient energy to replenish the energy storage system to the maximum energy state level, the artificial minimum energy state level is lowered.
The energy storage controller preferably is further programmed to control the energy storage system by restricting the raising of the artificial minimum energy state level beyond a predetermined level below the maximum energy state level. It is also preferred that the energy storage controller is further programmed to control the energy storage system by restricting the lowering of the artificial minimum energy state level beyond a predetermined level above the actual minimum energy state level.
The energy storage system may comprise energy storage systems of any type capable of energy discharge acceptance events such as those selected from the group of: (1) at least one ultracapacitor and (2) at least one hydraulic cylinder. The energy storage system may also comprise an internal combustion engine and a generator adapted to provide energy to the energy storage system, such as electric energy.
The present invention also includes a method of controlling an energy storage system, the method comprising: providing an energy storage system electrically coupled to a power conversion device, the energy storage system adapted to recapture energy from the power conversion device so as to be capable of discharging and recapturing energy through a series of discharge and energy acceptance events, and having a maximum energy state level and an actual minimum energy state level; and the energy storage system providing energy to the power conversion device, and the power conversion device adapted to supply energy to the energy storage system; and an energy storage controller programmed to control the energy storage system by setting an artificial minimum energy state level to an initial level above the actual minimum energy state level, and, during a series of discharge and energy acceptance events, to be able to adjust the artificial minimum energy state level such that:
(a) in cases where a discharge and energy acceptance event results in the acceptance of insufficient energy to recharge the energy storage system to the maximum energy state level, raising the artificial minimum energy state level; and
(b) in cases where a discharge and energy acceptance event results in the acceptance of sufficient energy to recharge the energy storage system to the maximum energy state level, lowering the artificial minimum energy state level.
The present invention also includes a method and apparatus by which power is controlled in a hybrid electric vehicle such that high levels of performance and efficiency are realized. The invention relates specifically to the alternate energy source and optimization of its use.
The present invention includes a method and apparatus developed to optimize the use of energy in a hybrid vehicle application from the hybrid energy storage device.
The method and apparatus of the present invention is particularly useful with energy storage devices where the state of charge is readily determined by an easily measured attribute. Ultracapacitors and hydraulic storage cylinders are examples of the types of energy storage devices to which the present invention may be applied.
The state of charge, or energy level, is proportional to the voltage of the ultracapacitor or the pressure of the hydraulic cylinder. The method and apparatus of the present invention is particularly well-suited to hybrid vehicle applications where the hybrid power is primarily utilized during acceleration and deceleration.
The present invention is particularly well-suited to hybrid electric vehicle applications where the hybrid power is primarily used during acceleration and deceleration. The method includes three fundamental features which may be illustrated with respect to a parallel hybrid electric vehicle using storage of the type described above: (1) energy is expended from the hybrid energy storage device at a predetermined rate until a minimum energy level target is reached, whereupon the energy storage device is later replenished with energy from the vehicle. There is an equilibrium of energy expended to that replenished that will result; (2) the minimum energy target is continuously adjusted such that that equilibrium can be maintained at a higher power state of the storage device; and (3) replenishing the energy storage device with both the kinetic energy from the vehicle while decelerating, and with energy drawn from the primary power source of the vehicle during opportune events (i.e., typically when the vehicle is cruising or coasting, such as when moving downhill or otherwise not in need of accelerating power).
In one aspect of the invention, during vehicle acceleration, when hybrid energy is desired, energy is expended from the hybrid energy storage device at a pre-determined rate until a target minimum energy level is reached. Subsequently, during deceleration the recapture of energy from the kinetic energy of the vehicle to replenish the storage device is maximized. The more energy recovered in the energy storage device prior to a given acceleration event, the more energy that can be expended in that acceleration event.
In contrast to earlier methods, the method of the present invention features a system that is self-adjusting and will seek equilibrium with the energy balance of what is expended and replenished. The method of the present invention does not utilize fixed relationships between the hybrid storage level and vehicle state such as, for example, energy level and vehicle speed. Accordingly, changes to the energy and power requirements of the vehicle due to variations in terrain, drive cycle, vehicle weight, tire pressure, and the like will not adversely affect its performance. The hybrid drive following the minimum target level strategy will naturally adjust its contribution to maintain consistent vehicle performance and operator/passenger feel.
The rate at which energy is expended from the energy storage device may be any rate, so long as it is consistent.
The present invention also includes the adjustment of the minimum energy target level continuously so the energy storage device and corresponding power conversion system maintain a higher power state at equilibrium. For the energy storage devices described herein, the power is a product of the potential and flow. Accordingly, for a given flow, a higher potential will provide higher power.
There are two advantages to maintaining a higher potential. First, available hybrid power will be more consistent with peak power despite drive cycles with low vehicle kinetic energy. Second, for powers less than peak power of the system, a higher potential means less flow required. For energy storage devices such as Ultracapacitors and hydraulic cylinders, and the corresponding power conversion systems, lower flow means less energy loss as heat and thus higher efficiency. In addition, lower heat loss means that cooling systems do not work as hard.
In operation, each time the hybrid vehicle comes to rest at zero speed, and accounting for settling time of the storage device, the energy level of the storage device can be evaluated to see if the level has reached maximum capacity. If not, the minimum energy target level can then be raised. If so, the minimum target level can be lowered. This process repeats until equilibrium is reached. Anticipating disruptions to equilibrium will maximize the effectiveness of the strategy.
In another aspect of the invention, the higher energy level of the storage device prior to acceleration, the more that can be expended by way of hybrid assist. Striving for maximum hybrid contribution, two approaches as presented for increasing the amount of energy available prior to an acceleration event, beyond what is recovered during vehicle deceleration with regenerative braking.
One approach is to “siphon” power from the primary power source while it is operating at high efficiency or while it could be made to operate more efficiently. That is, to charge the energy storage system from the primary power source at a nominal rate that is just enough so as not to drastically alter its operation. Examples of operating points ideally suited for siphoning include when the vehicle is cruising at a steady state where fuel economy is relatively high and when the vehicle is stopped with the engine at idle doing little work with fixed operating overhead.
A small siphon charge over a period of time can significantly increase the energy level of the storage device. As a means to preserve storage capacity for the vehicle deceleration with regenerative braking, a target energy level is set below which siphoning is permitted. The target energy level is established in some relation to the kinetic energy of the vehicle.
The other approach is to simulate the drag normally associated with internal combustion engines at closed throttle through the use of regenerative braking. By applying a moderate level of regenerative braking when the operator lifts from the accelerator pedal, the vehicle will decelerate slightly and the energy storage device will be charged at a low rate.
The present invention allows for consistency in the power output during acceleration which is proportionate to apparent power demand.
The method and apparatus of the present invention feature the function of certain algorithms for system control. These algorithms use real-time inputs from the vehicle systems and provide real-time outputs for control of vehicle systems. The principal function of the present invention is to supplement the primary power source in a manner that is relatively transparent to the operator while preserving standard, consistent vehicle performance. This allows for consistent feel to the operator and the passengers as the vehicle accelerates and decelerates.
The present invention features a control algorithm that maintains the state of charge of the energy storage device (such as one or more ultracapacitors) within a pre-determined range as the vehicle proceeds through a number of energy expending and recapture events which may involve net energy loss or net energy gain.
The present invention is an improvement over the technology described in U.S. Pat. Nos. 6,484,830 and 6,651,759, which are hereby incorporated herein by reference, and which may be used with hybrid electric vehicles and drive systems as described therein as an example.
In general terms, the present invention includes a hybrid electric vehicle comprising a drive train; an electric motor for driving the drive train; a power unit electrically coupled to the electric motor; an electric energy storage system electrically coupled to the electric motor, the electric energy storage system adapted to recapture energy from the braking of the vehicle so as to be capable of discharging and recapturing energy through a series of discharge and energy recapture events, and having a maximum charge level and an actual minimum charge level; and wherein the power unit and the electric energy storage system provide electricity to the electric motor for powering the vehicle; and an electric energy storage controller programmed to control the electric energy storage system by setting an artificial minimum charge level to an initial level above the actual minimum charge level, and, during a series of discharge and energy recapture events, to be able to adjust the artificial minimum charge level such that: (a) in the case where a discharge and energy recapture event results in the recapture of insufficient energy to recharge the electric energy storage system to the maximum charge level (e.g., the energy discharged in an acceleration and the energy recaptured from braking after that acceleration), the artificial minimum charge level is raised; and (b) in the case where a discharge and energy recapture event results in the recapture of sufficient energy to recharge the electric energy storage system to the maximum charge level, the artificial minimum charge level is lowered.
It is preferred that the electric energy storage controller is further programmed to control the electric energy storage system by restricting the raising of the artificial minimum charge level beyond a predetermined level below the maximum charge level.
It is preferred that the electric energy storage controller is further programmed to control the electric energy storage system by restricting the lowering of the artificial minimum charge level beyond a predetermined level above the actual minimum charge level.
The present invention may be applied to any energy storage system, although, in the case of a hybrid electric vehicle, it is preferred that the energy storage system is a bank of Ultracapacitors, and that this system be used in association with an internal combustion engine and a generator adapted to charge the energy storage system with electrical energy.
Another aspect of the present invention is a hybrid electric vehicle comprising a drive train; an electric motor for driving the drive train; a power unit electrically coupled to the electric motor; an electric energy storage system electrically coupled to the electric motor, the electric energy storage system adapted to recapture energy from the braking of the vehicle so as to be capable of discharging and recapturing energy through a series of discharge and energy recapture events, and having a maximum charge level and an actual minimum charge level having a working range therebetween and which working is defined at its lower end by an artificial minimum charge level; and wherein the power unit and the electric energy storage system provide electricity to the electric motor for powering the vehicle; and an electric energy storage controller programmed to control the electric energy storage system by setting an artificial minimum charge level to an initial level above the minimum charge level, and, during a series of discharge and energy recapture events, to be able to adjust the artificial minimum charge level such that the working range of the electric energy storage system is biased toward the maximum charge level over the series of discharge and energy recapture events.
The present invention also includes a method of controlling an energy storage system, the method comprising: providing an electric energy storage system electrically coupled to the electric motor, the electric energy storage system adapted to recapture energy from the braking of the vehicle so as to be capable of discharging and recapturing energy through a series of discharge and energy recapture events, and having a maximum charge level and an actual minimum charge level; and wherein the power unit and the electric energy storage system provide electricity to the electric motor for powering the vehicle; and an electric energy storage controller programmed to control the electric energy storage system by setting an artificial minimum charge level to an initial level above the actual minimum charge level, and, during a series of discharge and energy recapture events, to be able to adjust the artificial minimum charge level such that: (a) in the case where a discharge and energy recapture event results in the recapture of insufficient energy to recharge the electric energy storage system to the maximum charge level, raising the artificial minimum charge level; and (b) in the case where a discharge and energy recapture event results in the recapture of sufficient energy to recharge the electric energy storage system to the maximum charge level, lowering the artificial minimum charge level.
The method of the present invention thus maintains the charge level of the energy storage device, such as an ultracapacitor, at a level in the higher end of the charge range over time.
Other objects, features, and advantages of the present invention will become apparent to those skilled in the art from the following detailed description and accompanying drawings. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration and not limitation. Many modifications and changes within the scope of the present invention may be made without departing from the spirit thereof, and the invention includes all such modifications.